Autonomic Regulation
NS regulation of the heart originates in the Cardiovascular Centre in the Medulla Oblongata. This area directs output by increasing or decreasing the frequency of nerve impulses in both the sympathetic and parasympathetic divisions of the ANS. The cardiovascular centre in the brain stem receives input from a variety of sensory receptors.
Among those are proprioceptors, chemoreceptors and baroreceptors.
Sympathetic nerve impulses reach the heart via spinal nerves exiting the thoracic spine cord. Parasympathetic nerve impulses reach the heart via right and left vagus nerves (CNX) and terminate in the SA node, AV node and atrial myocardium.
Chemical Regulation
Chemicals can influence both the basic physiology of the heart and the heart rate. For example: hypoxia (lower O2), acidosis (lower pH), alkalosis (higher pH) all can depress cardiac activity. Some hormones and cations have a major effect on the heart. Hormones - Epinephrine and Norepinephrine from the adrenal medullae enhance the hearts pumping effectiveness increasing both HR and contractility. Thyroid hormones also enhance cardiac contractility and increase HR (sign of hyperthyroidism is tachycardia or elevated resting HR). Cations - Since concentration differences b/t extracellular and intracellular cations (Na+ and K+) are crucial for production of APs in all nerve and muscle fibres, it can be deducted that ionic imbalances can quickly compromise pumping effectiveness of the heart. Specifically, K+, Ca++, and Na+.
249
Made with FlippingBook Publishing Software